In a compact teleconference device, the speaker and microphone are typically placed close to each other. When the distance between the speaker and the microphone is short, omnidirectional microphones pick up considerable echo. Unidirectional microphones also pick up substantial echo, especially in low frequencies, due to the proximity effect. Bidirectional microphones with their axis oriented perpendicular to the speaker, reject echo signals at a significantly better than omnidirectional or unidirectional microphones.
In teleconference devices, small circular arrays of bidirectional microphones may use gain sharing/mixing to cover a room with multiple talkers. However, conventional gain sharing/mixing may result in poor performance due when using bidirectional microphones. Bidirectional microphones pick up sound from either end of the microphone with opposite polarity. When mixing the output of two bidirectional microphones, the polarity of each signal may cause the total output to cancel out a meaningful signal.